On HTML/RichText emails it is appended as white text therefore you may not see it, but it can always be seen at the very bottom of "some" email if you use plain text.

I have noticed it on many of my works emails, to/from different sources and if you google for it you get a lot of entries of people emailing mailing lists for various reasons with it appended to their email.

Having this within my email causes no pain or issue... I'd just really like to know what it is

I looked long and hard at this question, but couldn't find any conclusive answers. My guesses at this point is it's some kind of ID that either Mimecast or services that use Mimecast use.
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Eugene van der MerweAug 27 '12 at 14:34

I agree with @EugenevanderMerwe's guess: I suspect Mimecast uses it when scanning emails, perhaps as an indicator of completion (to avoid rescanning emails multiple times?). I notice that the term is often inserted into emails as <font color=white>itevomcid</font>, using a tag (which is apparently ignored in some forums) to attempt to make it invisible.
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kmoteAug 28 '12 at 21:37

@Karan your search skills are better than mine. I just did a search on that term and found many Mimecast e-mails, I never saw the community topic. You should post your comment in the answer box, because you have the correct answer.
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Eugene van der MerweAug 29 '12 at 8:16